Unable to retrieve the printer list. Error message received from manager:
Connection to CUPS server failed. Check that the CUPS server is correctly installed and running. Error: the IPP request failed for an unknown reason.

here is the output from stoping and restarting cups: 
[root@localhost ckwall]# /etc/init.d/cups stop
Stopping cups:                                             [  OK  ]
[root@localhost ckwall]# /etc/init.d/cups start
Starting cups:                                             [  OK  ]